Active compounds for crop protection and for the protection of materials, i.e. substances which, even at low concentration, may display physiological activity in the plant or in a harmful organism, for example insecticides, fungicides and herbicides, but also growth regulators, are frequently formulated and applied in the form of aqueous active compound preparations. Frequently, such formulations are aqueous concentrates which, prior to their application, are diluted by addition of a large amount of water to the desired application concentration (so-called “spray liquor”).
A general problem in the case of aqueous active compound preparations is the generally poor solubility of the active compounds in water, which is frequently less than 5 g/l at 23° C./1013 mbar. Accordingly, aqueous formulations of such active compounds are heterogeneous systems where the active compound is present as an emulsified and/or dispersed phase in a continuous aqueous phase. For stabilizing these systems, which are metastable per se, it is customary to employ emulsifiers or dispersants. However, their stabilizing action is frequently unsatisfactory, so that the active compound may separate out, for example cream or sediment, in particular if the aqueous formulation is stored for a relatively long period of time at elevated temperature and/or at highly variable temperatures or close to freezing point. This problem is particularly pronounced if the active compound has a tendency to crystallize.
Organic solvents, too, are frequently used for preparing aqueous formulations of water-insoluble active compounds. Thus, water-miscible solvents are frequently used as solubilizers, i.e. to increase the solubility of the active compound in the aqueous phase. Water-immiscible solvents, in turn, serve to convert an active compound which is solid at the application temperature into a liquid phase which can then be emulsified. In contrast to the solid active compound, because of the solvent, the active compound is dissolved in the emulsion in molecular form and more readily available and more effective on application. However, owing to the known problems caused by VOC, the use of organic solvents is, for reasons related to work hygiene, because of environmental aspects and in some cases also for toxicological reasons, not desirable.
A further disadvantage of conventional aqueous active compound preparations is the relatively large particle size of the active compound particles and active compound droplets suspended and emulsified, respectively, in the aqueous phase, whose size is generally in the region of several μm. However, what is desired are aqueous formulations in which the active compound is present in the most highly dispersed form possible, firstly to ensure uniform distribution in the formulation and thus better handling and dosing properties and to increase simultaneously the bioavailability of the active compound in the formulation. What is desired here are formulations in which the mean particle sizes in the heterogeneous active compound-comprising phase are below 1500 nm, preferably below 1000 nm, in particular below 600 nm and especially below 300 nm.
There have been various proposals to formulate water-insoluble active compounds in the form of aqueous micro- or nanoemulsions (see, for example, WO 02/082900, WO 02/45507 and WO 99/65301). In contrast to conventional macroemulsions/suspensions which are usually milky/turbid and in which the particle sizes in the dispersed phase are significantly above 1 μm, the active compounds in the clear to opaque micro- or nanoemulsions are present in finely divided form, with particle sizes considerably below 1000 nm to up to 10 nm or below [see D. J. Shaw, Introduction to Colloid and Surface Chemistry, Butterworths, London 1986, p. 273]. However, the preparation of such micro- or nanoemulsions requires relatively large amounts of emulsifier and of organic solvents. However, the high proportion of emulsifiers does not only contribute to costs but can also lead to problems when applying the formulations. Solvents for their part are unwanted for reasons of work hygiene and for cost reasons. A further problem of such microemulsions is their instability with respect to breakdown.
Furthermore, there have been various descriptions of aqueous polymer/active compound preparations which are obtained by free-radical aqueous emulsion polymerization of a monomer emulsion, where the active compound is present in the monomer droplets of the monomer emulsion to be polymerized (see U.S. Pat. No. 3,400,093 and FR 1598644). However, this process is limited to active compounds which are readily soluble in the monomers. In general, these are substances which are liquid at room temperature.